Field of the Invention
The present invention relates to an image-capturing apparatus (hereinafter referred to as “a camera body”) and an accessory apparatus such as an interchangeable lens communicable with each other.
Description of the Related Art
In an accessory-interchangeable camera system including a camera body to which an accessory apparatus is detachably attachable, the camera body and the accessory apparatus communicate with each other for controlling the accessory apparatus from the camera body and for providing, from the accessory apparatus to the camera body, data required for controlling the accessory apparatus.
In particular, when an interchangeable lens is used for capturing a moving image to be recorded or a live-view moving image to be displayed, smooth lens control in synchronization with image-capturing periods is required, so that it is necessary to synchronize image-capturing times in the camera body with control times in the interchangeable lens. Thus, the camera body is required to complete receipt of the data from the interchangeable lens and transmission of various commands and requests to the interchangeable lens in one image-capturing period. However, an increase in amount of the data to be received by the camera body from the interchangeable lens and a reduction of the image-capturing period (that is, an increase in a frame rate) require a large data volume communication in a shorter time. Japanese Patent Laid-Open No. 2010-237514 discloses a camera system having a one-directional communication mode (hereinafter referred to as “a high-speed mode”) and a bidirectional communication mode (hereinafter referred to as “a low-speed mode”). In the high-speed mode, a one-directional communication channel for data transmission from a camera body to an interchangeable lens and another one-directional communication channel for data transmission from the interchangeable lens to the camera body are used in parallel, and thereby burst communication as continuous data communication capable of communicating a large amount of data by full-duplex communication is performed. On the other hand, in the low-speed mode, one communication channel is used whose communication direction is switched between transmission of a request from one of the camera body and the interchangeable lens to the other and transmission of data corresponding to the request from the other to the one.
However, when the camera system disclosed in Japanese Patent Laid-Open No. 2010-237514 falls into a situation where performing the continuous data communication is difficult due to an insufficient processing speed of a microcomputer provided in the interchangeable lens or the camera body in the high-speed mode, the camera system cannot suspend the transmission of data, which may make the data communication therebetween impossible.
In order to avoid such impossibility of the data communication, it is necessary to set as a communication standard a sufficiently low data communication speed with respect to performances of various possible microcomputers or to reduce the amount of data to be transmitted. However, these methods cannot effectively use the performances of microcomputers provided to the camera body and the interchangeable lens, which makes it impossible to achieve high-speed data communication. On the other hand, if a buffer provided to the camera body for storing data transmitted from the interchangeable lens has an insufficient capacity with respect to a large amount of data transmitted from the interchangeable lens in one burst communication, the buffer cannot store the entire transmitted data.